This is a good question. My kids are very involved in the presidential election. Before our state primary I bought each a t-shirt for our chosen candidate--they're as convinced as I am, or even more so. We've watched the debates together and, if I find that our candidate is giving a speech we can watch online, I let them know. Sometimes they huddle around my laptop to watch and listen. I've also taken a couple of my kids canvassing with me.
My youngest is 13, and I've tried to gently tell him about the financial crisis. When he asks me to buy X, Y, or Z I tell him that we need to be more careful in spending our money because I'm not sure what will happen. He doesn't understand that part, but he accepts that he can't have what he always wants--I've always raised my kids to accept that, anyway.
We just had a holiday (I'm a Muslim) and this year I lowered the amount I would spend on each kid. They still got what they really wanted though. They just had to prioritize. And I didn't buy any DVDs, as I usually do, but yesterday we made a run to Blockbuster and the library (which has rental movies for a dollar). That was good enough.
The most important thing you can do, I think, is to talk to your kids. And because you have older stepdaughters, I'm sure you're very much in tune with age-appropriate discussion. If in doubt, I think you should ask them. They were kids not too long ago and I bet they remember.